The present invention relates to a fan drive and, more particularly, to a cooling system which uses a constant viscous coupling and a variable viscous coupling to drive the fan.
A vehicle powered by an internal combustion engine generally requires an air circulation system in the engine compartment to avoid overheating of the engine. The air may be forced throughout the engine compartment to cool the engine directly, and/or may be directed into a heat exchanging system which dissipates heat from an engine coolant system. A fan is the most commonly used device to provide airflow, and the fan is normally powered by the engine crankshaft, directly or through an intermediate linkage (xe2x80x9cfan drivexe2x80x9d).
Because the engine compartment is often crowded, the fan and its associated fan drive mechanisms should be compact and simple to service. In addition, vehicle manufacturers must balance governmental noise emissions regulations with the need for engine cooling, so a fan having a variable speed is used to reduce the fan noise by slowing the fan when the engine compartment needs less cooling. For these reasons, it is common for a variable viscous coupling/clutch to provide power transmission in the fan drive.
An example of a cooling system using a variable viscous coupling is disclosed in the undated document titled xe2x80x9cC543/035/99: Radial fan and externally controlled viscous clutch for radial truck cooling system CCS(trademark)xe2x80x9d, authored by W. Zobel et al. (hereafter referenced as C543). The cooling system of C543 includes a variable viscous coupling which is used to transmit power from an input shaft to a fan. However, a variable viscous coupling may have trouble producing the initial torque needed to start the fan turning due to the flow rate of the viscous fluid filling the coupling. Also, should the viscous fluid escape the single viscous coupling system, the fan may experience a loss of power that can lead to engine overheating.
Various prior art viscous couplings have included two or more primary disks in a single housing. This arrangement does not have as much capacity to dissipate heat produced in operation from the primary disks through the multi-disk housing as does the more common single-disk housing arrangement, since the multi-disk housing has much less surface area per disk than does the single-disk housing. Also, the single-disk configuration is commonly available in a range of predetermined sizes and capacities and may therefore be more efficiently provided than the multi-disk version.
The present invention is directed to overcoming one or more of the problems as set forth above.
In an exemplary embodiment of the present invention, a multiple coupling fan drive is disclosed. The multiple coupling fan drive includes: an input shaft adapted to rotate selectively about a longitudinal axis, a constant viscous coupling including a constant primary disk rotated by the input shaft, and a variable viscous coupling including a variable primary disk rotated by the input shaft.
In an exemplary embodiment of the present invention, a method of operating and powering a fan is disclosed. The method includes the steps of: selectively rotating an input shaft, selectively rotating a constant viscous coupling with the input shaft, selectively rotating a variable viscous coupling with the input shaft, and rotating the fan with at least one of the constant viscous coupling and the variable viscous coupling.
In an exemplary embodiment of the present invention, a cooling system is disclosed. The cooling system includes: a fan, a temperature sensor adapted to produce a temperature value, and a multiple coupling fan drive. The multiple coupling fan drive includes: an input shaft adapted to rotate selectively about a longitudinal axis responsive to the temperature value, a constant viscous coupling adapted to rotate the fan and including a constant primary disk rotated by the input shaft, and a variable viscous coupling adapted to rotate the fan and including a variable primary disk rotated by the input shaft.